1. Field of the Invention
The present invention relates to an apparatus and method for scanning documents with high resolution. Also, the present invention relates to an image scanning and copying apparatus of the type in which an original such as a document is two-dimensionally scanned to produce image signals and an image is formed by driving a plurality of printing elements such as ink jet heads by means of the image signals.
2. Description of the Prior Art
Recently, a remarkable progress has been made in the image scanning and copying apparatus. At present, aiming at further development of the technique, many efforts are being made to increase the resolution of image detection and print to speed up the image detecting and printing operation and to simplify the signal processing system used in the course of image detection and printing.
The printing system most widely used in the above mentioned type of image forming apparatus uses an array of printing elements arrayed in one single row. The array of printing elements is moved in the direction normal to the row of the printing elements to two-dimensionally scan a document and then form an image thereof by only one scanning. However, this conventional printing system has a disadvantage. It is impossible for this system to record such image which has a higher resolution than the pitch of the printing elements. For example, when ink jet nozzles are used as the printing elements, the possible minimum space between nozzles is 0.25 mm for any array of ink jet nozzles available according to the prior art. Therefore, the maximum recording resolution attainable by it is 4 image points/mm. Such printing resolution is obviously not enough to record images contained in common documents. The resolution desired for this purpose is at least 12 image points/mm. To realize this objective, it is also required to provide a detection apparatus which is able to detect high resolution image point signals.
A high resolution copying apparatus has been disclosed in U.S. Pat. No. 4,112,469 (Japanese Patent Application laid open No. 136,835/1978). The known apparatus uses a sensor array comprising N (in number) photo diodes arranged at regular intervals. The sensor array detects an original document in a manner of interlaced scanning with high resolution. Recording is carried out using a printing head comprising N nozzles arrayed in regular intervals in the same interlaced fashion as used at the time of detection scanning to effect high resolution recording.